A hybrid-type display apparatus is disclosed e.g. in a Japanese patent laid-open No. 11-52366 and a Japanese patent laid-open No. 11-183892. The hybrid-type image display apparatus performs a reflective display using external light by reflecting on a semi-transmission reflective layer on the back side the external light incident from the front side when the external light having sufficient brightness (such as natural light or interior light) is obtained, and performs a transmittive display using illumination light which is a back light arranged on the back side of the image display apparatus when the external light having sufficient brightness is not obtained. This hybrid-type image display apparatus basically comprises a display panel having pixels arranged in a matrix form and displaying images by reflecting external light from the front side or by having illumination light from the back side transmit therethrough, and a flat-type back light arranged at the back of the display panel and radiating the illumination light.
Such a hybrid-type image display apparatus is preferably applied particularly to a display section of a portable information terminal device or a portable telephone terminal device. As the external light can be used when it is bright around, it is not necessary to turn on the back light, and thus electric power consumption can be reduced. In the portable information terminal device or the portable telephone terminal device in which electric power supply is limited, it is the most important point to reduce the electric power consumption.
Conventionally, an LED or a fluorescent tube is used as the back light. Accordingly, the thickness of the back light cannot be 2 mm or thinner. Although there will be raised an increasing demand for reducing the thickness of a portable device in the future, the conventional back light cannot satisfy the demand of reducing its thickness. Thus, there is a need for newly developing a back light structure suitable for a hybrid-type image display apparatus. Meanwhile, an EL is used as a conventional back light, as well as the LED or the fluorescent tube, and such a back light is disclosed in a Japanese patent laid-open No. 11-316376. The art disclosed in this laid-open patent is not used in a hybrid-type image display apparatus.